add gears.table.cycle_value (#2942)

lib/gears/table.lua

@@ -1,6 +1,13 @@
 ---------------------------------------------------------------------------
 --- Table module for gears.
 --
+-- Examples
+-- =======
+--
+-- Using `cycle_value`, you can cycle through values in a table.
+-- When the end of the table is reached, `cycle_value` loops around to the beginning.
+-- @DOC_text_gears_table_cycle_value_EXAMPLE@
+--
 -- @utillib gears.table
 ---------------------------------------------------------------------------
 
@@ -217,6 +224,41 @@ function gtable.clone(t, deep)
     return c
 end
 
+--- Get the next (or previous) value from a table and cycle if necessary.
+--
+-- If the table contains the same value multiple type (aka, is not a set), the
+-- `first_index` has to be specified.
+--
+-- @tparam table t The input table.
+-- @param value A value from the table.
+-- @tparam[opt=1] number step_size How many element forward (or backward) to pick.
+-- @tparam[opt=nil] function filter An optional function. When it returns
+--  `false`, the element are skipped until a match if found. It takes the value
+--  as its sole parameter.
+-- @tparam[opt=1] number start_at Where to start the lookup from.
+-- @return The value. If no element match, then `nil` is returned.
+-- @treturn number|nil The element (if any) key.
+-- @staticfct gears.table.cycle_value
+function gtable.cycle_value(t, value, step_size, filter, start_at)
+    local k = gtable.hasitem(t, value, true, start_at)
+    if not k then return end
+
+    step_size = step_size or 1
+    local new_key = gmath.cycle(#t, k + step_size)
+
+    if filter and not filter(t[new_key]) then
+        for i=1, #t, step_size do
+            local k2 = gmath.cycle(#t, new_key + i)
+            if filter(t[k2]) then
+                return t[k2], k2
+            end
+        end
+        return
+    end
+
+    return t[new_key], new_key
+end
+
 --- Iterate over a table.
 --
 -- Returns an iterator to cycle through all elements of a table that match a

spec/gears/table_spec.lua

@@ -42,6 +42,35 @@ describe("gears.table", function()
         end)
     end)
 
+
+    describe("table.cycle_value", function()
+        it("nil argument", function()
+            local t = { "a", "b", "c", "d" }
+            local f = gtable.cycle_value(t, "a")
+            assert.is.same(f, "b")
+        end)
+        it("with step size", function()
+            local t = { "a", "b", "c", "d" }
+            local f = gtable.cycle_value(t, "a", 2)
+            assert.is.same(f, "c")
+        end)
+        it("b filter", function()
+            local t = { "a", "b", "c", "d" }
+            local f = gtable.cycle_value(t, "a", 1, function(i) return i == "b" end)
+            assert.is.equal(f, "b")
+        end)
+        it("e filter", function()
+            local t = { "a", "b", "c", "d" }
+            local f = gtable.cycle_value(t, "a", 1, function(i) return i == "e" end)
+            assert.is.equal(f, nil)
+        end)
+        it("b filter and step size", function()
+            local t = { "a", "b", "c", "d" }
+            local f = gtable.cycle_value(t, "b", 2, function(i) return i == "b" end)
+            assert.is.equal(f, nil)
+        end)
+    end)
+
     describe("table.find_keys", function()
         it("nil argument", function()
             local t = { "a", "b", c = "c", "d" }

tests/examples/awful/widget/layoutlist/popup.lua

@@ -63,10 +63,10 @@ local modkey = "mod4" --DOC_HIDE
         stop_key = {"Escape", "Super_L", "Super_R"},
         keybindings = {
             {{ modkey          } , " " , function()
-                awful.layout.set(gears.table.iterate_value(ll.layouts, ll.current_layout, 1))
+                awful.layout.set(gears.table.cycle_value(ll.layouts, ll.current_layout, 1))
             end},
             {{ modkey, "Shift" } , " " , function()
-                awful.layout.set(gears.table.iterate_value(ll.layouts, ll.current_layout, -1), nil)
+                awful.layout.set(gears.table.cycle_value(ll.layouts, ll.current_layout, -1), nil)
             end},
         }
     }

tests/examples/text/gears/table/cycle_value.lua

@@ -0,0 +1,10 @@
+--DOC_GEN_OUTPUT --DOC_HIDE
+local gears = require("gears") --DOC_HIDE
+
+local res = {"a", "b", "c", "d", "e"}
+
+for i=1, #res do
+    local k = res[i]
+    local v = gears.table.cycle_value(res, k, 1)
+    print(v)
+end